1. Field of the Invention
The present invention relates to a mercury-free light source, and more particularly to a cold cathode luminescent field emission device which is environmentally friendly and energy efficient.
2. Related Art
Light sources for daily living are usually incandescent lamps or fluorescent tubes. Incandescent lamps have a long history since the first incandescent lamp invented by Thomas Edison in 1879. However, because an incandescent lamp emits light by incandescence of a tungsten filament, most of electric energy used is converted into heat and wasted. Therefore, a main drawback of the incandescent lamp is low energy efficiency.
A conventional fluorescent tube generally includes a transparent glass tube, a phosphor layer coated on an inner surface of the glass tube, and a certain amount of mercury vapor filled in the glass tube. The mercury vapor in the glass tube is excited by an electrical discharge applied in the glass tube. The excitation of the mercury vapor produces ultraviolet (UV) rays, irradiate the phosphor layer on the inner surface of the glass tube. This causes the phosphor layer to emit visible light. Compared with incandescent lamps, fluorescent tubes are more energy efficient. However, a main drawback of fluorescent tubes is that they contain mercury, which is a toxic substance harmful to human beings and the environment. It is anticipated that fluorescent tubes and other electric devices containing mercury will be forbidden in some regions of the world in the future, such as in the European Union.
Therefore, what is needed is a light source that is mercury-free and energy efficient.